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Calculate secondary fault current in transformer

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Calculate secondary fault current in transformer

(OP)
Hi.

How can I calculate the fault current in the secondary of a transformer when I know the following information:

Fault infeed level 200MVA, 10.5kV fault current on primary side. Transformer is 12.5MVA, 11/3kV with 10% impedance (on rating).

How can I calculate the current on the secondary, without using the mva method, so without calculating the source impedance and adding it to the transformer impedance on a given base.

Thanks

RE: Calculate secondary fault current in transformer

Hi. Do you want something like this? (maybe I made it a bit complicated)

[img https://imgur.com/a/4IxWt]

PS. I don't know how to use this "add picture" thing

JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

RE: Calculate secondary fault current in transformer

(OP)
Hi. The answer is clearly correct. I guess not sure how by basically calculating the fault level of the infeed in parallel with the maximum fault level of the transformer you get the right answer?! Any more explanation around this please?

Thank you for your help

RE: Calculate secondary fault current in transformer

Hi

I never did the mathematical analysis but I know that the analogy with series / parallel circuits is valid (in reverse).

If you have elements (network, transformers, generators) in series, you must calculate Scc doing the count as 'resistances in parallel', and vice versa if you have elements in parallel

Maybe you can do the analysis and show it to us;)

Regards,

JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

RE: Calculate secondary fault current in transformer

(OP)
Hi. Yeah I just can't find a formula for the relationship between the current in the primary and the current in the secondary side that does not involve converting to MVA. Is there a formula that utilises the transformer winding ratio and the impedance to give the secondary current if the primary fault level current is known?

Thanks

RE: Calculate secondary fault current in transformer

Hi,

If there is one, I do not know it.
I guess you may get it working with the expressions that I give you and their equivalents.

JBC
.......
"The more I read, the more I acquire, the more certain I am that I know nothing"

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